Sanguine Bond

Whenever you gain life, target opponent loses that much life.

Gravecrawler

This creature can't block.
You may cast this card from your graveyard as long as you control a Zombie.

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Dina, Soul Steeper

Whenever you gain life, each opponent loses 1 life.
{1}, Sacrifice another creature: Dina gets +X/+0 until end of turn, where X is the sacrificed creature's power.

Exquisite Blood

Whenever an opponent loses life, you gain that much life.

Marauding Blight-Priest

Whenever you gain life, each opponent loses 1 life.